Selectively flexible catheter and method of use

ABSTRACT

Catheter assembly including an elongate shaft comprising a thermoplastic polymer such as a thermoplastic shape memory polymer having a pre-selected glass transition temperature (Tg) and a means for heating the thermoplastic polymer, wherein the thermoplastic polymer is in a rubbery state at temperatures above the glass transition temperature and is in a glassy state at temperatures below the glass transition temperature. The elongate shaft may be selectively heated and cooled to provide sufficient flexibility and retention during a medical procedure.

RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser.No. 11/004,544, filed Dec. 3, 2004, the entire disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The invention generally relates to catheters and more specifically tocatheters having improved flexibility to navigate very tortuous vesselswhile maintaining sufficient stability at a distal site.

BACKGROUND OF THE INVENTION

Intravascular catheters are used in a wide variety of relativelynon-invasive medical procedures. Such intravascular catheters may beused for diagnostic or therapeutic purposes. Generally, an intravascularcatheter allows a physician to remotely perform a medical procedure byinserting the catheter into the vascular system of the patient at alocation that is easily accessible and thereafter navigating thecatheter to the desired target site. Vascular passageways distal of theinsertion point, such as the neurovascular system, are often narrow andquite tortuous. Furthermore, in order to navigate through the patient'stortuous vascular system, intravascular catheters must be very flexible.If a catheter is sufficiently flexible to reach and pass through thetortuous vasculature, the catheter may lack sufficient column strengthor stability to remain in position while, for example, subsequenttreatment devices are advanced through the catheter.

It is desirable for an intravascular catheter having sufficientflexibility to reach tortuous vasculature be able to retain a sufficientamount of rigidity while positioned at the target site in order toprovide stability and back-out support during a subsequent medicalprocedure.

SUMMARY OF THE INVENTION

The invention is directed to a catheter having sufficient flexibility toreach remote areas of the vasculature, yet providing rigidity whilepositioned at the target site to provide back-out support whileadditional treatment devices are advanced through the catheter. Such acatheter, for example, may provide sufficient flexibility to navigate toremote vessels, such as the neurovascular system, yet offer stabilitywhile delivering a therapeutic device, such as an embolic coil, to atarget site.

Accordingly, one embodiment of the invention is a catheter including anelongate shaft comprising a shape memory material such as a shape memorypolymer, having a pre-selected glass transition temperature (Tg). Theshape memory polymer retains relatively stiff, glassy characteristics attemperatures below the glass transition temperature and becomesrelatively flexible and rubbery at temperatures above the glasstransition temperature.

In one embodiment of the invention, a means for heating the shape memorypolymer is provided. Such means for heating may include light energy,electrical resistance heating, RF electromagnetic heating, ultrasonicheating, radiation energy, and fluid conduction heating, to name a few.For example, a guidewire may extend through the catheter lumen. Theguidewire may be subjected to thermal energy by a heating means. Forexample, the guidewire may be connected to an electrical source, whereinthermal energy is created by electrical resistance along the guidewire.Alternatively, or additionally, a coil may be provided in the catheter,wherein the thermal energy is created by such means as electricalresistance along the coil.

The present invention further includes a method for placement andretention of a catheter within a vasculature. A catheter within thescope of the invention may be heated above a glass transitiontemperature (Tg) to become flexible and rubbery. While in a flexiblestate, the catheter may be positioned within the vasculature, conformingto the curvature of the vasculature. Once positioned in the vasculature,the catheter may then be cooled below a glass transition temperature(Tg) to become stiffer. While in the stiff, glassy state, the catheterretains the curvature formed in the catheter following the curvature ofthe vasculature pathway. By retaining this curvature, the catheterprovides enhanced retention and back-out support during a medicalprocedure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a plan view of a catheter according to the invention;

FIG. 2 is a cross-sectional view of a portion of a catheter inaccordance with the invention;

FIG. 3 is a cross-sectional view of a portion of a catheter inaccordance with the invention;

FIG. 4 is a cross-sectional view of a portion of a catheter inaccordance with the invention;

FIG. 5 is a cross-sectional view of a portion of a catheter assemblyselectively heating a portion of a catheter in accordance with theinvention;

FIG. 6 is a cross-sectional view of a portion of a catheter assemblyselectively heating a portion of a catheter in accordance with theinvention; and

FIG. 6A is an enlarged view of FIG. 6 showing thermal energy generatedfrom a coil for selectively heating a portion of a catheter inaccordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

All numeric values are herein assumed to be modified by the term“about”, whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the terms “about” may include numbers thatare rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numberswithin that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4,and 5). As used in this specification and the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontent clearly dictates otherwise. As used in this specification andthe appended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

The following detailed description should be read with reference to thedrawings in which similar elements in different drawings are numberedthe same. The detailed description and the drawings, which are notnecessarily to scale, depict illustrative embodiments and are notintended to limit the scope of the invention.

As shown in FIG. 1, the invention generally relates to a catheter 10including an elongate shaft 20 extending from a proximal end 12 to adistal end 14. The catheter 10 may include a hub 16 near the proximalend 12 and a distal tip 18 near the distal end 14.

FIG. 2 is a cross-sectional view of a portion of the catheter 10according to one embodiment of the invention. The portion of thecatheter 10 shown in FIG. 2 is a distal portion of the catheter 10including the distal tip 18; however, similar features depicted in FIG.2 may be located at more proximal locations of the elongate shaft 20instead of, or in addition to, those located along a distal portion ofthe catheter 10.

The elongate shaft 20 may include a polymer layer 30. The polymer layer30 may be formed of a material such as high-density polyethylene (HDPE),low-density polyethylene (LDPE), silicone, fluoropolymer, liquid crystalpolymer (LCP), polyimide, polyamide, polyester, polyethylene (PE),polypropylene, polyvinyl chloride (PVC), polyfluorocarbon, polyurethane,polysulfone, ethyl vinyl acetate (EVA), polyether block amide (PEBAX),styrene-ethylene/butylenes-styrene (SEBS), styrene-butadiene-styrene(SBS), polyethylene terephthalate (PET), and their mixtures, alloys,blends, copolymers, and block copolymers. Preferably, polymer layer 30may comprise a thermoplastic polymer having a glass transitiontemperature. A thermoplastic polymer, in contrast with a thermosetpolymer, may have the capabilities of being repeatedly softened byheating and hardened by cooling within a temperature range correspondingto a temperature such as a glass transition temperature. Therefore, athermoplastic polymer may be repeatedly heated and reshaped. On theother hand, a thermoset polymer, once initially formed by crosslinking,irreversibly retains that pre-shaped form and may not be softened byheating to take on a new form.

More preferably, polymer layer 30 may comprise a thermoplastic shapememory polymer, such as a polyurethane-based polymer, having apre-selected glass transition temperature. The shape memory polymerretains relatively stiff, glassy characteristics at temperatures belowthe glass transition temperature and becomes relatively flexible andrubbery at temperatures above the glass transition temperature.Preferably, the glass transition temperature is selected to be greaterthan the body temperature of the patient during treatment. The glasstransition temperature may be greater than about 37° C., for example.The glass transition temperature may be selected in the range of about38° C. to about 80° C., or more preferably in the range of about 50° C.to about 80° C. Most preferably, the glass transition temperature may beselected in the range of about 60° C. to about 70° C. Shape memorypolymers are preferred to other polymers due to their relatively sharptransition from a glassy state to a rubbery state. Additionally, thehardness variation between the glassy state and the rubbery state may bein the range of 200%. For example, a thermoplastic shape memory polymerwithin the scope of the invention may have a durometer hardness of 75-80D in the glassy state and a durometer hardness of 25-30 D in the rubberystate. Additionally, shape memory polymers may possess greater integritythan other potential polymers when subjected to multiple iterationsacross the glass transition temperature.

A thermoplastic shape memory polymer may be characterized as a polymerthat undergoes a phase transformation at a manufactured temperature,such as the glass transition temperature of the polymer. After thematerial is polymerized, the polymer is molded into its memory shape.The polymer is rubbery at temperatures above the glass transitiontemperature, whereby the polymer is flexible and may easily be flexedinto an arbitrary form. The polymer retains this arbitrary form when thetemperature falls below the glass transition temperature. Below theglass transition temperature, the polymer becomes relatively stiff inthe glassy state. If the polymer is reheated above the glass transitiontemperature, the polymer will return to its original memory shape ifunrestrained.

The polymer layer 30 may extend substantially the entire length of theelongate shaft 20 or a portion thereof. The polymer layer 30 may extendalong a distal portion of the elongate shaft 20 to provide a regionhaving improved flexibility and retention capabilities. As shown in FIG.2, polymer layer 30 may include an inner layer 32 and an outer layer 34.However, polymer layer 30 may comprise a single layer.

A reinforcement member 36 may be disposed along at least a portion ofthe polymer layer 30. Reinforcement member 36 may be disposed along aninner surface of the polymer layer 30 or along an outer surface of thepolymer layer 30. As shown in FIG. 2, reinforcement member 36 may bedisposed between at least a portion of the inner layer 32 and the outerlayer 34 of polymer layer 30. Alternatively, reinforcement member 36 maybe disposed within at least a portion of polymer layer 30. Reinforcementmember 36 may be a heat conductive reinforcement member. Reinforcementmember 36 may be a coil helically wound along at least a portion of thelength of elongate shaft 20. Alternatively, reinforcement member 36 maybe a braid woven along at least a portion of the length of the elongateshaft 20. Reinforcement member 36 may comprise one or more filaments 38.Filaments 38 may have a circular cross-sectional profile or filaments 38may have a relatively flat cross-sectional profile such as is shown inFIG. 3. It is contemplated that filaments 38 may have any perceivablecross-sectional profile.

Elongate shaft 10 may include an outer tubular member 50 disposed aboutat least a portion of polymer member 30. Some examples of some suitablematerials may include stainless steels (e.g., 304v stainless steel),nickel-titanium alloys (e.g., nitinol, such as super elastic or linearelastic nitinol), nickel-chromium alloys, nickel-chromium-iron alloys,cobalt alloys, nickel, titanium, platinum, or alternatively, a polymermaterial such as a high performance polymer, or other suitablematerials, and the like.

Outer tubular member 50 may include a plurality of apertures 55 formedalong the length of outer tubular member 50 to increase the flexibilityof the elongate shaft 20 to a desired level. Apertures 55 may be slots,slits, grooves, helical cuts, or the like. The spacing, depth and typeof apertures 55 may be varied to control the flexure profile andtorsional stiffness of the outer tubular member 50. The spacing ofapertures 55 may vary gradually along outer tubular member 50, or maychange incrementally. Apertures 55 may extend through the wall of theouter tubular member 50, or they may extend only partially through thewall. It is contemplated that at least some of the apertures extendthrough the wall of the outer tubular member 50. Apertures 55 may bemicromachined into the outer tubular member 50 by electrostaticdischarge machining (EDM), chemical milling, ablation, laser cutting,saw cutting, grinding, etching, or the like. Apertures 55 may extendsubstantially the full length of the elongate shaft 20, or apertures maybe positioned along selected portions of the elongate shaft 20 whereincreased flexibility is desired. Such techniques for creating apertures55 along the outer tubular member 50 are discussed in detail in U.S.Patent Publication 2003/0069522 to Jacobsen et al., as hereinincorporated by reference in its entirety.

The elongate shaft 20 may include an inner liner 60. Preferably, innerliner 60 comprises polytetrafluoroethylene (PTFE).Polytetrafluoroethylene is a preferred material because it creates asmooth, low friction surface for the passage of other devices or fluidsthrough the lumen 40 of elongate shaft 20. In an alternate embodiment,inner liner 60 may comprise materials including, but not limited to,thermoplastics, high performance engineering resins, fluorinatedethylene propylene (FEP), polymer, polyethylene (PE), polypropylene(PP), polyvinylchloride (PVC), polyurethane, polyether-ether ketone(PEEK), polyimide, polyamide, polyphenylene sulfide (PPS), polyphenyleneoxide (PPO) polysulfone, nylon, or perfluoro(propyl vinyl ether (PFA).

A distal tip 18 may be disposed at the distal end 14 of elongate shaft20. Distal tip 18 may comprise any of a number of suitable polymers orpolymer blends. For example, distal tip 18 may comprise a polyetherblock amide (PEBAX®). Preferably distal tip has a low durometer hardnessin the range of about 40 A about 60 D. As shown in FIG. 2, reinforcementmember 36 extends into at least a portion of distal tip 18. However,distal tip 18 may extend distal of the reinforcement member 36 or abutreinforcement member 36 at the distal end 14 of the elongate shaft 20.Preferably, distal tip 18 may extend approximately 5 cm. or less.

An alternate embodiment is shown in FIG. 3. Elongate shaft 20 mayinclude a reinforcement member 136 including at least one filament 138having a flat ribbon profile. Reinforcement member 136 may be a helicalcoil or a braid member. A polymer layer 30 may be disposed adjacent thereinforcement member 136 and may extend substantially the entire lengthof the elongate shaft, or any portion thereof. As shown in FIG. 3, thepolymer layer 30 may be disposed about the reinforcement member 136. Aninner liner 60, as discussed above, may be disposed in the lumen 40 ofthe elongate shaft 20. Outer tubular member 50 having a plurality ofapertures 55 may be disposed about at least a portion of the polymerlayer 30. Preferably, outer tubular member extends substantially theentire length of the elongate shaft 20. As shown in FIG. 3, polymerlayer 30 may extend distal of the reinforcement member 136 and/or theouter tubular member 50 to define a distal tip 118.

Another embodiment of the invention is shown in FIG. 4. Elongate shaft20 may include a reinforcement member 36 disposed between an outer layer34 and an inner layer 32 of polymer layer 30. The reinforcement member36 and polymer layer 30 may extend to the distal end 214 of the elongateshaft 20. A distal tip 218 may abut the distal end 214 of the elongateshaft 20 and extend distally to provide a soft atraumatic tip. As shownin FIG. 4, elongate shaft 20 or a portion thereof need not include anouter tubular member 34.

In one embodiment of the invention, a means for heating the shape memorypolymer is provided. Such means for heating may include light energy,electrical resistance heating, RF electromagnetic heating, ultrasonicheating, radiation heating, or fluid conduction heating, to name a few.For example, a heat conductive member 70 may be positioned along atleast a portion of the polymer layer 30. Heat conductive member 70 maybe a conductive wire connected to an electrical supply (not shown),wherein resistance in heat conductive member 70 creates thermal energy90. Heat conductive member 70 may comprise at least one filament 38 ofreinforcement member 36 or a guidewire 80, for example. As shown in FIG.5, a guidewire 80 may extend through the lumen 40 of elongate shaft 20.The guidewire 80 may be connected to an electrical source (not shown),wherein thermal energy 90 is transferred, for example by electricalresistance, along the guidewire 80. Alternatively, or additionally, asshown in FIG. 6, at least one filament 38 of reinforcement member 36 maybe provided along the elongate shaft 20, wherein thermal energy 90 iscreated by electrical resistance along the reinforcement member 36. Ascan be better shown in FIG. 6A, reinforcement member 36 may transmitthermal energy 90 to at least a portion of the polymer layer 30. It iscontemplated that heat conductive member 70 may transfer thermal energy90 to the polymer layer 30 by alternate means such as through RFheating, ultrasonic heating, laser heating, or the like.

A method of changing the flexibility of a catheter as described abovefor placement and retention in a vasculature will now be described.Prior to insertion in a patient's vasculature, elongate shaft 20 may bein its more rigid, glassy state, wherein polymer layer 30 is at atemperature below the glass transition temperature. Polymer layer 30 maybe subjected to a thermal energy source, wherein thermal energyincreases the temperature of the polymer layer above the glasstransition temperature. The thermal energy source may be RF heating,electrical resistance heating, a chemical reaction, ultrasonic waves,radiation heating, fluid conduction heating, or light energy, to name afew. Above the glass transition temperature, the elongate shaft 20 mayhave increased flexibility for navigating a tortuous vasculature. Whilein the more flexible, rubbery state above the glass transitiontemperature, the elongate shaft 20 may be easily navigated through thevasculature, wherein the elongate shaft 20 takes on an arbitrarycurvature complementing the vasculature pathway taken by the catheter 10to a target site within the patient's body. Therefore, elongate shaft 20need not have a pre-shaped curvature in order to navigate a tortuousvasculature and conform to a selected pathway. Once positioned at atarget site in the vasculature, the polymer layer 30 of elongate shaft20 is cooled below the glass transition temperature, wherein the polymerlayer 30 transitions to a rigid, glassy state. The polymer layer 30 maybe cooled naturally by the body as the temperature of the polymer layerequalizes with the body temperature, or the polymer layer 30 may beartificially cooled by other means such as by flushing the catheter 10with a cooler fluid such as saline. As the polymer layer 30 is cooledbelow the glass transition temperature, the elongate shaft 20 retainsits arbitrary curvature within the vasculature. Below the glasstransition temperature, the elongate shaft 20 may be form cast to thecurvature of the pathway through the vasculature. In this rigidconfiguration, the elongate shaft 20 exhibits increased stability andback-out support for the catheter 10. During a subsequent medicalprocedure, an additional medical device or devices may be deliveredthrough the elongate shaft 20 to the target site. For example, emboliccoils may be passed through the catheter 10 to a target site within thevasculature. The rigid state of the curvature retains the elongate shaft20 at the target site during such a medical procedure and prevents theelongate shaft 20 from shifting in the vasculature. Since the elongateshaft 20 is in the rigid, glassy state while positioned in thevasculature, it is advantageous for the polymer layer 30 to have a glasstransition temperature greater than the body temperature of the patient.In other words, for use in a human being, the glass transitiontemperature is preferably greater than about 37° C.

At the conclusion of a medical procedure, the elongate shaft 20 may bereheated above the glass transition temperature of the polymer layer 30.Once in its flexible, rubbery state, the elongate shaft may easily bewithdrawn from the vasculature or repositioned at a subsequent targetsite within the body. Subsequent cycles of heating and cooling theelongate shaft may be performed as necessary during a medical procedureto provide selective flexibility and stability to the catheter.

Those skilled in the art will recognize that the present invention maybe manifested in a variety of forms other than the specific embodimentsdescribed and contemplated herein. Accordingly, departure in form anddetail may be made without departing from the scope and spirit of thepresent invention as described in the appended claims.

1. A method for treating tissue at a target location in a patient's bodyusing a catheter, the catheter comprising a thermoplastic shape memorypolymer having a glass transition temperature, the method comprising inthe following order the steps of: (a) heating at least a distal portionof the catheter to raise a temperature of the polymer in the distalportion above the glass transition temperature to thereby render thedistal portion of the catheter into a flexible state; and (b)positioning the distal portion of the catheter at the target location inthe patient's body, wherein, after the distal portion is positioned atthe target location, the polymer in the distal portion cools to atemperature lower than the glass transition temperature to therebyrender the distal portion into a rigid state.
 2. The method of claim 1,wherein, when the distal portion of the catheter is in its flexiblestate and positioned at the target location, the distal portion of thecatheter assumes a shape complementary of a shape of the targetlocation.
 3. The method of claim 2, wherein, after the polymer in thedistal portion of the catheter cools to a temperature lower than theglass transition temperature, the distal portion of the catheter retainsthe shape complementary of the shape of the target location.
 4. Themethod of claim 1, further comprising the step of (c) administering atreatment through the catheter to tissue at the target location.
 5. Themethod of claim 4, further comprising the steps of (d) heating at leastthe distal portion of the catheter while it is at the target location tothereby raise the temperature of the polymer in the distal portion abovethe glass transition temperature and render the distal portion of thecatheter into its flexible state, and (e) withdrawing the catheter fromthe target location with the distal portion of the catheter in itsflexible state.
 6. The method of claim 1, wherein step (a) comprisesheating a thermally conductive member disposed in or adjacent to thedistal portion of the catheter.
 7. The method of claim 6, wherein thethermally conductive member is selected from the group comprising a heatconductive coil, a heating guidewire, a light energy heating member, anelectrical resistance heating member, an RF electromagnetic heatingmember, an ultrasonic heating member, a radiation heating member, and afluid conduction heating member.
 8. The method of claim 1, wherein step(b) comprises actively cooling the polymer in the distal portion of thecatheter below the glass transition temperature.
 9. The method of claim8, wherein actively cooling the polymer in the distal portion comprisesflushing the catheter with a liquid.
 10. The method of claim 1, whereinthe glass transition temperature is greater than a body temperature ofthe patient.
 11. The method of claim 1, wherein the glass transitiontemperature is greater than about 37° C.
 12. The method of claim 1,wherein the glass transition temperature is between about 38° C. andabout 80° C.
 13. The method of claim 1, wherein the glass transitiontemperature is between about 50° C. and about 80° C.
 14. The method ofclaim 1, wherein the glass transition temperature is between about 60°C. and about 70° C.
 15. The method of claim 1, wherein the targetlocation is a vascular location.
 16. A method for positioning a distalportion of a catheter at a target location in a patient's body, thecatheter comprising a thermoplastic shape memory polymer having a glasstransition temperature, the method comprising in the following order:passing current through an electrical resistance heating member disposedin or adjacent to the distal portion of the catheter to thereby raise atemperature of the polymer above the glass transition temperature andrender the distal portion into a flexible state; and positioning thedistal portion at the target location in the patient's body, wherein,after the distal portion is positioned at the target location, thepolymer in the distal portion cools to a temperature lower than theglass transition temperature to thereby render the distal portion into arigid state.
 17. The method of claim 16, wherein the catheter comprisesan inner layer and an outer layer, and the electrical resistance heatingmember is disposed between the inner and outer layers.
 18. The method ofclaim 16, wherein, when the distal portion of the catheter is in itsflexible state and positioned at the target location, the distal portionof the catheter assumes a shape complementary of a shape of the targetlocation.
 19. The method of claim 18, wherein, after the polymer in thedistal portion of the catheter cools to a temperature lower than theglass transition temperature, the distal portion of the catheter retainsthe shape complementary of the shape of the target location.
 20. Themethod of claim 17, wherein the inner and outer layers each comprise thethermoplastic shape memory polymer.